Listeria monocytogenes is a facultative intracellular gram positive bacterium. The genus Listeria contains seven species: L. monocytogenes, L. innocua, L. ivanovii, L. seeligeri, L. welshimeri, L. grayi, and L. murrayi. Virulence of these species is quite diverse and L. monocytogenes is considered to be the only pathogenic species for humans. Pregnant women, new-born and immunocompromised patients are especially susceptible to infection. Another species of the genus, L. ivanovii, is also pathogenic but infections by this species are extremely rare and only affect animals.
L. monocytogenes is increasingly recognized as responsible for severe infections in both animals and humans. Although discovered in 1926, L. monocytogenes has only recently been recognized as a food pathogen after the tracing of epidemics to contaminated food (Kvenberg, 1988). Prolonged food conservation times and new eating habits have led to a real need for rapid detection of L. monocytogenes, which is able to grow in hostile conditions such as 4.degree. C. and in up to 7% NaCl (Seeliger and Jones, 1986).
To avoid human infection, food sources have routinely been screened for the presence of Listeria organisms. Potential food sources infected with any species of Listeria have routinely been discarded to avoid infecting the consumer because of the time and expense involved in determining whether the infecting organisms are or are not pathogenic. Thus, there is a need for a means for identifying and readily and efficiently distinguishing between pathogenic and non-pathogenic Listeria species. This information is also necessary to determine the course of treatment of suspected Listeria infections and for the development of data for epidemiological studies.